1. Field of the Invention
The present invention relates to oil and water separators generally and more particularly to oil and water separators employing coalescers.
2. Discussion of the Background
Concerns over possible contamination of the water supply through the presence of oil and other contaminants in wastewater has risen dramatically in recent years. Many governmental authorities require such contaminants to be removed before the wastewater may be discharged into the environment. The level of contamination permitted by government regulation varies. Typically, oil in such wastewater should be less than 25 parts per million, and preferably 5-10 parts per million or less.
Oil/water separating systems are the preferred method of treating oil-contaminated wastewater. An example of such a gravity oil/water separator is described in U.S. Pat. No. 5,204,000 to Steadman, et al. One known type of oil/water separator is the gravity oil/water separator. The gravity separators function by allowing gravity to separate the oil from the water. A serious problem associated with gravity separators is that they require a large volume and/or long processing times to accomplish the separation. This makes such separators costly and impractical for many applications.
The aforementioned problems associated with gravity separators has led many to incorporate coalescers into oil and water separators. One well-known type coalescer is formed from oleophilic and/or hydrophobic materials for attracting oil and/or repelling water as oil-contaminated water passes through the coalescer. An example of coalescers of this type are the vertical tube coalescers available from AFL Industries, Inc. These coalescers are described in U.S. Pat. No. 4,333,835 to Lynch. Such coalescers have been used by Xerxes Corp., the assignee of the present invention, in underground wastewater storage tanks. Tanks such as these have generally been designed under the assumption that the oil separation gradient is linear; that is, that the amount of oil in wastewater decreases linearly as the wastewater passes through the coalescers. Thus, the coalescers have generally been arranged in a single continuous block. While tanks with such arrangements of coalescers have proven effective in removing oil from wastewater in smaller areas and/or more quickly than gravity separators, these tanks are expensive.
What is needed is a more economical oil and water separator.
The present invention meets the above-identified need to a great extent by providing a storage tank with an oil and water separator in which the frontal area of the coalescers is increased relative to known arrangements of coalescers in oil and water separators. It has been discovered through experimentation that the oil separation gradient is not linear, but rather exponential. That is, the vast majority of the oil/water separation occurs at the first portion of the coalescer that is exposed to wastewater, and oil removal decreases in efficiency as wastewater moves through the coalescer. Therefore, by arranging the coalescers such that the frontal surface area of the coalescers is increased, the efficiency of the coalescers is increased. In some preferred embodiments, the coalescers are arranged in a bank with free flow fluid paths between the coalescers in the bank, each of the paths being closed by a baffle on one end and open on an opposite end, and the baffles are arranged such that the open and closed ends of paths alternate. In other preferred embodiments, the coalescers are arranged in a tubular fashion and fluid flows from the outside surface of the tube through the coalescers and out a central path.